Implantable stimulation devices are devices that generate and deliver electrical stimuli to body nerves and tissues for the therapy of various biological disorders, such as pacemakers to treat cardiac arrhythmia, defibrillators to treat cardiac fibrillation, cochlear stimulators to treat deafness, retinal stimulators to treat blindness, muscle stimulators to produce coordinated limb movement, spinal cord stimulators to treat chronic pain, cortical and deep brain stimulators to treat motor and psychological disorders, and other neural stimulators to treat urinary incontinence, sleep apnea, shoulder sublaxation, etc. The present invention may find applicability in all such applications, although the description that follows will generally focus on the use of the invention within a Spinal Cord Stimulation (SCS) system, such as that disclosed in U.S. Pat. No. 6,516,227.
Spinal cord stimulation is a well-accepted clinical method for reducing pain in certain populations of patients. As shown in FIGS. 1A and 1B, a SCS system typically includes an Implantable Pulse Generator (IPG) 100, which includes a biocompatible case 30 formed of titanium for example. The case 30 typically holds the circuitry and power source or battery necessary for the IPG to function, although IPGs can also be powered via external RF energy and without a battery. The IPG 100 is coupled to electrodes 106 via one or more electrode leads (two such leads 102 and 104 are shown), such that the electrodes 106 form an electrode array 110. The electrodes 106 are carried on a flexible body 108, which also houses the individual signal wires 112 and 114 coupled to each electrode. In the illustrated embodiment, there are eight electrodes on lead 102, labeled E1-E8, and eight electrodes on lead 104, labeled E9-E16, although the number of leads and electrodes is application specific and therefore can vary.
As shown in FIG. 2, the IPG 100 typically includes an electronic substrate assembly 14 including a printed circuit board (PCB) 16, along with various electronic components 20, such as microprocessors, integrated circuits, and capacitors mounted to the PCB 16. Two coils are generally present in the IPG 100: a data telemetry coil 13 used to transmit/receive data to/from an external controller 12; and a charging coil 18 for receiving power to charge the IPG's battery 26 using an external charger 50.
As just noted, an external controller 12, such as a hand-held programmer or a clinician's programmer, is used to wirelessly send data to and receive data from the IPG 100. For example, the external controller 12 can send programming data to the IPG 100 to dictate the therapy the IPG 100 will provide to the patient. Also, the external controller 12 can act as a receiver of data from the IPG 100, such as various data reporting on the IPG's status. The external controller 12, like the IPG 100, also contains a PCB 70 on which electronic components 72 are placed to control operation of the external controller 12. A user interface 74 similar to that used for a computer, cell phone, or other hand held electronic device, and including touchable buttons and a display for example, allows a patient or clinician to operate the external controller 12. The communication of data to and from the external controller 12 is enabled by a coil 17, which is discussed further below.
The external charger 50, also typically a hand-held device, is used to wirelessly convey power to the IPG 100, which power can be used to recharge the IPG's battery 26. The transfer of power from the external charger 50 is enabled by a coil 17′, which is discussed further below. For the purpose of the basic explanation here, the external charger 50 is depicted as having a similar construction to the external controller 12, but in reality they will differ in accordance with their functionalities as one skilled in the art will appreciate.
Wireless data telemetry and power transfer between the external devices 12 and 50 and the IPG 100 takes place via magnetic inductive coupling. To implement such functionality, coils in the IPG 100 and the external devices 12 and 50 act together as a pair. In case of the external controller 12, the relevant pair of coils comprises coil 17 from the controller and coil 13 from the IPG. While in case of the external charger 50, the relevant pair of coils comprises coil 17′ from the external charger and coil 18 from the IPG.
When data is to be sent from the external controller 12 to the IPG 100 for example, coil 17 is energized with an alternating current (AC). Such energizing of the coil 17 to transfer data can include modulation using a Frequency Shift Keying (FSK) protocol for example, such as disclosed in U.S. patent application Ser. No. 11/780,369, filed Jul. 19, 2007. For example, FSK communication can be centered around 125 KHz for example, with 121 kHz representing a logic ‘0’ and 129 kHz representing a logic ‘1’. Energizing the coil 17 produces a magnetic field, which in turn induces a current in the IPG's coil 13, which current can then be demodulated to recover the original data. Data telemetry in the opposite direction—from the IPG 100 to the external controller 12—occurs in essentially the same manner.
When power is to be transmitted from the external charger 50 to the IPG 100, coil 17′ is again energized with an alternating current to produce a non-modulated magnetic charging field. Such energizing is generally of a constant frequency (e.g., 80 kHz), and may be of a larger magnitude than that used during the transfer of data, but otherwise the physics involved are similar.
During charging, i.e., when the external charger 50 is producing the magnetic charging field, the IPG 100 can communicate data back to the external controller using Load Shift Keying (LSK). LSK is well explained in U.S. patent application Ser. No. 12/354,406, filed Jan. 15, 2009, and involves modulating the load at the IPG 100 to produce data-containing reflections detectable at the external charger 50. This means of transmitting data is useful to communicate data relevant during charging of the battery 26, such as whether charging is complete and the external charger 50 can cease production of the magnetic charging field. As one skilled in the art will understand, LSK data can only be communicated when the magnetic charging field is present, and can only be transmitted from the IPG 100 to the external controller 12. Moreover, LSK provides very low bit rates (e.g., 10 bits/second) and therefore the amount of data that can be sent by this means is limited.
Energy to energize coils 17 and 17′ can come from batteries in the external controller 12 and the external charger 50, respectively, which like the IPG's battery 26 are preferably rechargeable. However, power may also come from plugging the external controller 12 or external charger 50 into a wall outlet plug (not shown), etc.
As is well known, inductive transmission of data or power can occur transcutaneously, i.e., through the patient's tissue 25, making it particularly useful in a medical implantable device system. During the transmission of data or power, the coils 17 and 13, or 17′ and 18, preferably lie in planes that are parallel, along collinear axes, and with the coils as close as possible to each other. Such an orientation between the coils 17 and 13 will generally improve the coupling between them, but deviation from ideal orientations can still result in suitably reliable data or power transfer.
Although the external controller 12 and external charger 50 can be completely separate devices as shown in FIG. 2, other solutions have been proposed that integrate these two devices together to varying degrees. For example, in U.S. Patent Publication 2009/0118796, the circuitry for the external controller and the external charger are enclosed in a single housing. The coil for transferring data is enclosed within the housing, while the coil for transferring power to the IPG lies external to the housing, but is connected to the charging circuitry in the housing by a wire. In another solution disclosed in U.S. patent application Ser. No. 12/368,385, filed Feb. 10, 2009, the circuitry for the external controller and the external charger, and their associated coils, are enclosed within a single housing, which coils can be shared between the data telemetry and charging functions.
Even in these integrated controller/charger solutions, data transfer and power transfer do not take place at the same time. Therefore, if the patient needs to adjust the therapy program while the IPG is being charged for example, the patient is required to manually interrupt charging, manually activate the data telemetry circuitry, and then manually return to charging. The need to interrupt charging can occur in even simpler contexts such as if the patient merely wants to know the capacity of the battery while charging. Reporting of battery capacity in a manner reviewable by the patient is typically a data telemetry function under the control of external controller circuitry, and thus charging would need to cease to receive such data. Having to manually switch between charging and data telemetry functions is inconvenient for the patient. Not only may the patient need to manipulate a separate external controller and an external charger, the patient may also need to physically align those devices with the IPG to ensure good coupling between the coils in each of the devices. See, e.g., U.S. patent application Ser. No. 12/498,049, filed Jul. 6, 2009, discussing the importance of good coil alignment in this context. Such frustrations for the patient are especially needling when it is recognized that data telemetry may only take a short period of time (on the order of seconds or tenths of seconds) compared to the time needed the charge the IPG's battery (on the order of minutes or hours).
This disclosure provides embodiments of solutions to mitigate this problem.